Acoustical panels are well-known for use in ceilings, walls, room dividers, and anywhere sound absorbency is a potential problem. Acoustical tiles, also known as acoustical panels, ceiling tiles or ceiling panels, are well known in the building trades for providing a ceiling that is quickly installed, inexpensive and lightweight. The tiles are prepared from a slurry of fibers, fillers and binders, most frequently by either a casting process or a felting process.
In the water felting of such a slurry, a dispersion of a fiber, a filler, a binder and other ingredients flow onto a moving, porous support, such as that of a Fourdrinier or Oliver mat forming machine for dewatering. The dispersion dewaters first by gravity and then vacuum suction means. The wet basemat is dried in heated convection drying ovens forming a dried panel. Optionally, sound absorbance is increased by creating cavities in the product surface by, for example, needling, pinholing or embossing. The dried panels are then cut to the desired dimensions and optionally top coated, such as with paint, to produce finished acoustical tiles and panels.
Acoustical tile is also made by a wet pulp molded or cast process such as that described in U.S. Pat. No. 1,769,519. A molding composition that includes fibers, fillers, colorants and a binder is prepared for molding or casting the body of the tile. This mixture is placed upon suitable trays which have been covered with paper or a paper-backed metallic foil and then the composition is screeded to a desired thickness with a screed bar or roller. A decorative surface, such as elongated fissures, may be provided by the screed bar or roller. The trays filled with the pulp are then placed in an oven to dry or cure the composition. The dried sheets are removed from the trays and may be treated on one or both faces to provide smooth surfaces, to obtain the desired thickness and to prevent warping. The sheets are then cut into tiles of a desired size.
Current trends favor acoustic panels having a smooth, monolithic surface, similar to the adjoining drywall. During the production of cast panels, wool nodules in the panel tend to lend texture to the surface, thereby creating pores or pockets that are sound-absorbent. Many layers or coatings are known to provide a smooth surface, but these layers or coatings do not necessarily allow sound to pass through the coating and enter the acoustically absorbent panel. Any acoustically transparent coating for a panel should provide a smooth, monolithic, aesthetically pleasing finish. This finish is greatly preferred by users of such panels. The coating should maintain the current product features of being hard and durable, have a low volatile content and maintain a Class A classification.
Granulated or nodulated wool is mineral wool that is formed into pea-shaped pellets. Unlike conventional mineral wool fibers, it is convenient for measuring, pouring and transferring the material through hoppers or pipes. The nodulated wool is often used in the manufacture of base acoustical panels. U.S. Pat. No. 6,616,804, for example, teaches the use of nodulated wool in an acoustic base panel. More specifically, it discloses creating a nodulated overlay layer starting with baled wool and mixing at 40 rpm to form wool nodules in situ. The overlay is then joined with a wet fiberboard panel and the two layers are dried together to make an acoustical panel.
U.S. Pat. No. 6,443,256 to Baig, herein incorporated by reference, also teaches the use of nodulated wool overlay layer as a means of improving sound absorption. However, there are no teachings to suggest the use of degraded mineral wool in a coating as a means of providing a smooth coating. Preparation of some overlay layers can result in the need for special equipment to prepare and distribute the coating. Use of the overlay layer of the '804 patent requires at least perforating equipment and an oscillating screed blade. Purchase, installation and maintenance on this additional equipment increase the cost of the acoustical panel.
Another problem associated with the manufacture of acoustical panels with an acoustically transparent overlay layer is the cost incurred in purchasing, receiving, storing and dispensing a large number of ingredients for the base panel and the coating. As taught above, based mineral wool is useful in the panel, but nodulated wool fibers are used in the coating. These and other differences in the content of the overlay layer compared to the panel thus add to the cost of producing the finished acoustical panel.
It would be advantageous to find an acoustically transparent smooth coating for an acoustical panel. It would further be advantageous if the coating were thinly applied to the base mat using known coating equipment to minimize coating costs. Still further, it would be beneficial if the coating utilized many of the same components as the base panel to minimize the cost of obtaining and utilizing extra ingredients.